The invention is directed to a process for the production of very pure S-carboxymethyl-L-cysteine by reacting L-cystine in liquid ammonia with metallic sodium to form the disodium salt of L-cysteine, vaporizing the ammonia, reacting the disodium salt of L-cysteine with an aqueous solution of chloracetic acid and precipitating the S-carboxymethyl-L-cysteine formed by acidifying the reaction mixture.
A process of this type is described in Zhurnal Obshchei Khimii, Vo. 33 No. 9 pages 2888 to 2894. However, in the known process even if one works with the complete exclusion of air and pays attention to the reduction of the L-cystine employed proceeding quantitatively products are always obtained which contain up to 2 weight percent of L-cystine whose subsequent removal creates considerable difficulties because of the difficult solubility in water.
S-carboxymethyl-L-cysteine (SCC) is of pharmaceutical interest since it has mucous dissolving properties. Viscous mucous is rendered thin liquid by SCC and can thereby be more easily eliminated by coughings. Breathing is improved and made easier. SCC therefore is used for the production of medicines for treatment of bronchitis, tuberculosis, asthmatic illnesses as well as inflammations in the region of the throat and windpipe.
Since especially high purity requirements must be placed on pharmaceutical products the problem must be solved by the present invention of producing a very pure S-carboxymethyl-L-cysteine which is particularly free from L-cystine.